There is more to EULA's and ToS than what you guy's seem to be thinking.
Ein said:
Case for the former:
By clicking on 'I Agree' while purchasing, you basically executed a signature on a contract. You AGREED to bray like a hoarse donkey - possibly in addition to paying some money - in exchange for purchasing/using the product. Now, unless braying every 10 days is ILLEGAL in your country,you damn well better get brayin' or get ready to spend some quality time behind bars.
Let us say that you bought a software license whose EULA says that you need to bray like donkey every 10 days. Now not braying is not illegal in itself, but by not braying, you violated the EULA and the license that was issued to you stands null and void. (Remember that by paying, you didn't purchase the software, but a license to use the software and the same is subject to terms and conditions that the company imposed). If you continue using the software, you are basically using it without a license. You cannot be charged for not braying every 10 days, but you can definitely be charged for using software without a license.
Let us consider another example. The EULA says that the license is for use on one single computer at a time. You violated the EULA and installed the software on 10 of your friends computers using the same license for parallel use. The company may not charge you for violating the EULA clause, but they can charge you and your friends for illegal distribution/installation of software without a proper licenses.
Even in the worst case where the law cannot be used, the company can take suitable action on it by themselves. Lets say you paid for a service and broke the ToS, the company can stop your services, block your account etc and they won't have to pay you back either depending on how the ToS was framed.
Coming to the case of steam accounts, second hand sale of accounts is not permitted by Steam. They can ban any such account subject to them having proof that such a sale has happened. Lets say that TE allows sale of such accounts and some guy buys it and a couple of days later his account gets banned, What can the buyer do now?
The ban on such sales imposed by the TE Administration is fully justified, no matter how much people argue, things like these are gray areas and always reek of trouble.